From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The bedding of cones in a Phantom III Gearbox.
| Identifier | ExFiles\Box 94\1\ scan0340 | |
| Date | 24th February 1936 | |
| Phantom III Gearbox - Bedding of Cones. We have previously reported that the bedding of the top gear synchromesh cone does not correspond in use to that obtained when a bedding is taken when built up. It has been proved that the boring of the box is to within .001" in alignment, also that the cones show a 100% bedding taken on mandrels. On three boxes we have tested, the bedding of the top cone has shown it to be hard on the bottom edge, spreading to approximately a quarter upwards. The top of the cone showed no bedding. The third and second gear cones always show a full bedding. The result of this is that we have not experienced much difficulty in getting the synchromesh of the second and third to operate correctly, whereas the top has not functioned with the same amount of running. To obtain correct bedding of the top cone under running conditions, we have decreased the angle of the bronze cone by reducing the small dia. by .004". After that, this has given a full bedding of the cone. It is obvious from these results that there is a weakness in the first motion shaft bearings which allows the clutch shaft to pull the alignment out of truth. We are not making a 100% bedding of the cones by reducing the angle but simply increasing the area of friction to a certain amount. The result shown after test of a full bedding is due to one portion of the cone making a full contact, and actually a wrong impression is being obtained. We have tried two boxes with new cones not bedded in. 1st. - The cones had a fine thread turned on the surface. 2nd. - The cones left plain. Our experience is that the cones with the fine thread take only a short time to bed in and function correctly (excepting the top gear which we have previously reported upon). The plain cones have to be judiciously bedded in, and take considerably longer to get functioning correctly. There is more tendency for these cones to jam in operation. | ||